The present invention relates to a pressure-regulating device for a tank of a cryogenic fluid, especially a helium tank, which comprises a closed heating chamber extending through the wall of the tank and connected to this wall.
It furthermore relates to a plant for delivering fluid from a cryogenic tank.
The invention applies, for example, to the delivery of ultrapure helium for the microelectronics industry.
Cryogenic tanks have a very efficient thermal insulation. When gas is withdrawn from such a tank, the pressure, which is typically a few bar relative, drops because the heat influx is too low to compensate for the loss of fluid. Consequently, when gas is withdrawn, the pressure in the tank may drop excessively with respect to the requirements of the user network.
In order to keep the pressure in the tank constant, heat has to be supplied to the tank during withdrawal.
For this purpose, pressure-regulating devices for cryogenic tanks are known which use an electrical resistor as heating element, in combination with electrical safety means should there be a power failure. However, the known solutions are expensive if the emergency electrical supply has to operate for a long period.
The object of the invention is to provide an inexpensive pressure-regulating device which can provide a cryogenic tank with heat over a long period. The invention must furthermore guarantee that the contents of the container are not contaminated, even in the case of ultrapure fluids.
For this purpose, the subject of the invention is a pressure-regulating device characterized in that it includes a feed pipe suitable for feeding the heating chamber with a heating fluid having a temperature above the temperature of the said cryogenic fluid, and an exhaust pipe intended for discharging the heating fluid, each of the said pipes passing through an outer wall of the heating chamber.
The device according to the invention may include one or more of the following characteristics taken by themselves or according to any of their technically possible combinations:
the device includes a controlled valve inserted in the feed pipe and connected via its control part to a pipe for using the fluid in the tank so as to open the controlled valve when the pressure in the tank drops below a predetermined threshold;
the device includes second heating means, especially electrical resistors;
the second heating means are inserted into the heating chamber, preferably near the outlet of the feed pipe;
an insulating sleeve is provided on the inner wall of the tank, around a mid-section of the heating chamber, dividing the heating chamber into an insulated outer region and an uninsulated inner region;
the outlet of the feed pipe lies within the uninsulated region, near the inner end of the heating chamber;
the inlet of the exhaust pipe lies within the uninsulated region, near the insulated region;
the exhaust pipe is covered with thermal insulation means which extend from the outside of the heating chamber through its outer wall and approximately as far as the inlet of this pipe;
the heating gas has, under its conditions of use, a dew point below the temperature of the cryogenic fluid contained in the tank;
the cryogenic fluid and the heating gas consist of helium; and
the pipes are composed of a material which is a poor thermal conductor, especially an epoxy resin.
The subject of the invention is also a plant for delivering a fluid, comprising a tank for this fluid, which is in cryogenic form, equipped with a heating device as defined above, a use pipe, connecting the tank to a use station, and a heating gas source connected via a feed pipe to the heating device.